New Delhi , India -LRB- CNN -RRB- -- Seventy-two police officers were killed in an attack early Tuesday by suspected Maoists in eastern India , authorities said .

About 200 officers from the federal Central Reserve Police Force -LRB- CRPF -RRB- and a local police group were conducting a road inspection in Chhattisgarh state 's Dantewada district when the assault occurred , according to officials .

Dantewada 's top district administrator Reena Kangale told CNN that the attackers fired at the security officers and set off landmine explosions .

The attack and subsequent shootout lasted four hours , she said . Authorities launched rescue operations after the shootout ended , she added .

There was no immediate report of casualties on the Maoist side , Kangale added . The road inspection by the officers was being carried out ahead of a planned transportation of food to a camp of internally-displaced people , she explained .

India regards the communist rebels as its gravest internal security threat .

The Maoists , on the other hand , have claimed since the 1960s to be fighting for the dispossessed .

In February , India 's home minister P. Chidambaram acknowledged that more than 900 people , including almost 600 civilians , were killed in Maoist-related incidents in 2009 .

Some 200 suspected rebels were also slain as forces moved into areas under insurgent control , he said .

`` I am confident that the state governments concerned will gradually gain the upper hand and re-establish the authority of the civil administration , '' Chidambaram told an internal security conference on February 7 .

Indian Prime Minister Manmohan Singh , however , conceded last year that the nation 's fight with the Maoists had fallen short of objectives .

Maoists enjoy support not only in the poorest areas and in tribal communities but also among youth and the intelligentsia , officials suspect .

`` We have not achieved as much success as we would have liked in containing this menace , '' Singh said last September . `` It is a matter of concern that , despite our efforts , the level of violence in the affected states continues to rise . ''

In 2008 , 1,591 Maoist rebel attacks killed 721 people , according to government officials .

In addition to targeting police , alleged police informers and people they call `` class enemies , '' the rebels are also believed to be attacking infrastructure such as roads , bridges , railways , and power and telecommunication networks .

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72 police officers killed in an attack by suspected Maoists in eastern India

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Police holding road inspection in Chhattisgarh state 's Dantewada district before assault

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India regards the communist rebels as its gravest internal security threat

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Maoists have claimed since the 1960s to be fighting for the dispossessed